Sealing device for a centrifugal separator

ABSTRACT

A simple but still effective sealing device to separate two openings ( 4, 5 ), which are arranged at a distance from each other in the outer casing ( 3 ) of a shaft suspension unit ( 1 ), which supports a shaft ( 2 ) of a centrifugal separator in a bearing ( 8, 9 ), the shaft extending axially through at least one opening ( 4 ) into a space surrounding the shaft ( 2 ) in the outer casing ( 3 ). The sealing device is provided with sealing elements ( 12, 13 ), one connected to the outer casing ( 3 ) and one connected to the shaft ( 2 ), which surround the shaft ( 2 ) and divide the space in two departments ( 15, 16 ) connected to one opening each ( 4, 5,  respectively). The sealing elements form between themselves a narrow gap ( 14 ) surrounding the shaft ( 2 ), which prevents the flow of gas between the departments ( 15, 16 ). One of the sealing elements ( 12, 13 ) has a channel ( 21 ), which has an opening ( 23 ) in a central part of the gap ( 14 ), for the supply of a sealing liquid under pressure to the gap ( 14 ) in such a way that oil flows from the opening ( 23 ) through the gap ( 14 ) and out into the two departments ( 15, 16 ).

FIELD OF THE INVENTION

The present invention concerns a sealing device to separate twoopenings, which are arranged at a distance from each other in an outercasing of a shaft suspension unit, which is arranged during operation torotatably support a shaft of a centrifugal separator in at least onebearing, the shaft extending through at least one of said openings intoa space surrounding the shaft formed inside the outer casing.

BACKGROUND OF THE INVENTION

In shaft suspension units of this kind the shaft and parts connectedthereto and rotating with the shaft during operation entrain the air orother gas, which is located in this space. This air or gas contains oildrops in the form of an oil mist, which is used to lubricate bearingsarranged in the shaft suspension unit. By the rotation of the air theair pressure will be different in different parts of the space, whichmeans that the air pressure as a rule is different at the two openings.This causes an often very high air flow in through the one opening andout through the other opening, whereby the oil drops are lost for theirpurpose and pollute the surroundings of the shaft suspension unit.Furthermore, particles, bacteria etc. might enter the shaft suspensionunit and decrease the lifetime of the bearings or create colonies ofbacteria.

In U.S. Pat. No. 4,654,023 there is shown a centrifugal separator with ashaft suspension unit, which has an opening through which the shaft ofthe centrifugal separator extends. At this opening there is arranged amechanical sealing, which has a sealing element, which is connected tothe shaft, and a sealing element, which is connected to a stationaryouter casing of the shaft suspension unit, and which effectivelyprevents air or gas flow through the opening.

However, mechanical sealings of this kind are complicated, expensive andoften consume a high effect. Furthermore, they are worn out quickly atthe very high number of revolutions of centrifugal separators. Sincethey are difficult and time consuming to replace this involves highlabour and downtime costs.

SUMMARY OF THE INVENTION

The object of the present invention is to accomplish a sealing device ofthe kind initially described, which separates the two openings and issimple but still it prevents effectively an air flow through the twoopenings without being worn out and involve high labour and downtimecosts.

According to the present invention this is accomplished by providing asealing device of this kind with a first sealing element connected tothe outer casing and a second sealing element connected to the shaft,the sealing elements surrounding the shaft and together dividing thespace in two departments connected to one opening each and formingthere-between a narrow gap surrounding the shaft with no direct contactwith each other, the gap being arranged during operation to prevent aflow of gas between the two departments. One of the sealing elements isprovided with at least one channel, which has an opening in the centralpart of the gap, for the supply of a sealing liquid under pressure tothe gap during operation in such a way that sealing liquid flows out ofthe opening through the gap filled up with sealing liquid in a directionto and out into the two departments.

In a preferred embodiment of the invention the opening of the channel isarranged in a recess surrounding the shaft, the recess being formed inthe first sealing element and is open towards the second sealingelement.

Hereby a sealing device is accomplished, which effectively preventsairflow through the two openings.

Suitably, the sealing liquid consists of an oil, which continuously issupplied to the shaft suspension unit for the lubrication and/or coolingof the bearing. At least a portion of the oil, which flows out into adepartment from the gap, is conducted to the bearing located in thisdepartment. To accomplish this elements present in this department androtating with the shaft are used, the elements creating during operationan air circulation conducting the oil in the form of drops to thebearing.

In a special embodiment of the invention it comprises a conduit forreturn conducting a portion of the oil flowing out into one departmentfrom the gap directly to a collecting vessel.

BRIEF DESCRIPTION OF THE DRAWING

In the following the invention will be described in more detail withreference to the FIGURE on the attached drawing which schematicallyshows an axial section through an axial suspension unit in a centrifugalseparator, which is provided with an embodiment of a sealing deviceaccording to the present invention.

DETAILED DESCRIPTION

The shaft suspension unit 1 shown in the FIGURE supports the shaft 2 ofthe centrifugal separator. The shaft suspension unit 1 has an outercasing 3, which surrounds the shaft 2. In the axial end portions of theouter casing 3 there are arranged two openings 4 and 5, respectively,through which the shaft 2 extends. On one axial end of the shaft 2 arotor 6 is fixedly mounted and on the other axial end of it a belt drive7 is arranged for the driving of the shaft 2. The shaft 2 is journallysupported in a lower bearing 8, which essentially is connected directlyto the outer casing 3, and in an upper bearing 9, which is connected tothe outer casing 3 via two annular elastical elements 10 and 11. Theelastical elements 10 and 11 bear against a first annular sealingelement 12, which extends around the shaft 2 and connects the elasticalelements 10 and 11 to the upper bearing 9 at the same time as itconstitutes a bearing housing for the upper bearing 9. Radially insidethe first sealing element 12 there is arranged a second annular sealingelement 13, which is connected to the shaft 2 around the same andtogether with the first sealing element 12 forms an annular gap 14surrounding the shaft 2.

The sealing elements 12 and 13 divide a space inside the outer casing intwo departments 15 and 16, which are connected to one opening each 4 and5, respectively. To prevent the air or gas volumes from communicatingwith each other during operation via the gap 14 this is arranged to bekept filled up with liquid.

For this purpose a collecting vessel 17 for oil is arranged in the lowerpart of the shaft suspension unit 1, to which a conduit 18 is connected.This conduit is provided with a pump 19 and opens in at least one closedchamber 20 radially outside the first sealing element 12. In the firstsealing element 12 there is arranged a channel 21, which has an inletopening 22 in the chamber 20 and an opening 23 in a recess 24, which isformed in a central part of the first sealing element 12. The recess 24surrounds the shaft and is open towards the second sealing element 13.In the shown example the channel 21 is arranged during operation to beflown through by oil under pressure, which fills up the gap 14. The oilin the gap 14 prevents effectively air or other gas to flow between thetwo departments 15 and 16.

The amount of oil which flows through the gap 14 in direction towardsand out into the one or the other of the two departments 15 and 16 isdepending on how long and how narrow the gap 14 is in direction towardsthe one department 15 in relation to how long and narrow the gap is inthe direction towards the other department 16. Elements which rotatewith the shaft in the one department 15 creates an air circulation,which entrains oil, which flows out into this department 15, and bringsa portion of this oil to flow towards and through the bearing present inthis department, the upper bearing 9. The oil, which has passed throughthe upper bearing 9, is collected in the collection grove 25, which isopen radially inwardly and is connected to a return conduit 26, throughwhich collected oil flows back to a collecting vessel 17 via a liquidseal 27, which prevents air or gas circulation through the returnconduit 26. The most of the oil, flowing out of said one department 15is conducted back directly to the collecting chamber 17 via a by-passconduit 28, which in the shown example is connected to the returnconduit 26.

Oil is supplied to the gap 14 at such a high pressure during operationthat the gap is kept filled up at the pressure differences prevailingbetween the two departments 15 and 16. In certain cases the capillaryforces can be enough to keep the gap filled up whereas in other cases asubstantially higher pressure is demanded to keep the gap 14 filled upwith oil.

In the shown example the departments 15 and 16 communicate with theatmosphere surrounding the shaft suspension unit 1 via the respectiveopening 4 and 5 but it is quite possible within the scope of the presentinvention that they communicate via adhering opening to a more or lessclosed chamber.

What is claimed is:
 1. A sealing device to separate two openings (4, 5),which are arranged at a distance from each other in an outer casing (3)of a shaft suspension unit (1), which is arranged during operation torotatably support a shaft (2) of a centrifugal separator in at least onebearing (8, 9), the shaft (2) extending through at least one of saidopenings (4) into a space surrounding the shaft (2) formed inside theouter casing (3), comprising a first sealing element (12) connected tothe outer casing (3) and a second sealing element (13) connected to theshaft (2), the sealing elements (12, 13) surrounding the shaft (2) andtogether dividing the space in two departments (15, 16) connected to oneopening each (4, 5) respectively and forming them between a narrow gap(14) surrounding the shaft with no direct contact with each other, thegap being arranged during operation to prevent a flow of gas between thetwo departments (15, 16), at least one bearing (9), in which the shaftis rotatably supported in the outer casing, being arranged in one of thedepartments (15) and one of the sealing elements (12, 13) being providedwith at least one channel (21), which has an opening (23) in a centralpart of the gap (14), for the supply of an oil under pressure to the gap(14) during operation in such a way that oil flows out of the openingthrough the gap (14) filled up with oil in a direction to and out intothe two departments (15, 16) and means being provided to conduct atleast a portion of the oil flowing into said one of the departments (15)to the bearing (9) arranged in this department.
 2. A sealing deviceaccording to claim 1, wherein the opening (23) of the channel isarranged in a recess (24) surrounding the shaft (2) and is formed in onesealing element and is open towards the other sealing element (13).
 3. Asealing device according to claim 1 or 2, wherein the shaft (2) isjournally supported in the outer casing (3) by at least one bearing ineach department (15, 16) and has means provided to conduct at least aportion of the oil flowing out into one department (15, 16), to thebearing (8, 9) present in this department (15, 16).
 4. A sealing deviceaccording to claim 3, wherein said means consist of elements rotatingwith the shaft (2), the elements being arranged to create duringoperation a circulation of air entraining oil in the form of drops tothe bearing (9).
 5. A sealing device according to claim 3, furthercomprising a by-pass conduit for return conducting a portion of the oilflowing out into one department (15) from the gap (14) directly to acollecting vessel (17).
 6. A sealing device according to claim 4,further comprising a by-pass conduit for return conducting a portion ofthe oil flowing out into one department (15) from the gap (14) directlyto a collecting vessel (17).